CHESTERTOWN -- For long-time Kent County residents such as Walter Harris, it's one thing to grow accustomed to the window-rattling noise of routine munitions tests across Chesapeake Bay at Aberdeen Proving Ground in Harford County.

But it's another thing altogether to consider even a slim chance that a silent but poisonous cloud of chemicals could drift across the three miles of water separating APG from the Eastern Shore and touch down in Kent County.

As part of a congressional order to destroy an estimated 30,000 tons of obsolete mustard and nerve agents once considered crucial to the nation's weapons arsenal, the U.S. Army is planning to build a network of incinerators to burn the chemicals at eight government-owned locations -- including APG.

While the plan was long opposed by many Harford Countians who live near APG, residents of Kent County seem to have awakened recently to the fact that they live downwind of the 40-year-old stockpile.

"Aberdeen is no stranger to us," said Mr. Harris, one of the Eastern Shore's earliest and most vocal opponents of the incineration plan.

"We've had cracked window panes and windows put out of their tracks by the noise. We're not complaining about that," he said. "But we're not going to put up with this incinerator. This is just incredible."

So incredible to some Kent County residents, in fact, that organizers of a daylong symposium at Washington College tomorrow on the incinerator proposal are wondering whether the school's 600-seat theater is big enough for the expected turnout.

The meeting, which will feature appearances by Army and state officials, environmentalists and Kentucky residents fighting a similar incinerator there, has been promoted with posters depicting a wide-eyed child wearing a gas mask and clutching a Teddy bear.

Despite assurances from the Army's chemical experts that an accident involving mustard is highly unlikely -- and if one did happen the odds of it affecting Kent County are even more remote -- residents here are unconvinced.

Incinerator opponents received a major boost this week when the three-member Kent County Commission voted unanimously to join the fight against the Army plan.

"We reject the notion that any benefit -- be it economical, technological, environmental or political -- could be derived from the incineration of mustard agent," the commission said in a resolution.

And, in a move designed to erase any doubts about what side they were on, county officials announced they would no longer accept federal funds for drafting a local emergency plan to handle any accidents involving APG's existing mustard agent stockpile.

Instead, those Kent officials said, they will spend their own money to prepare evacuation plans or other protective measures.

Army studies have concluded that a serious chemical leak or spill at APG could affect humans and animals within an 11-mile radius of an incinerator.

Mustard agent is a liquid that freezes when the temperature falls below 58 degrees. Upon contact, it blisters the skin and eyes and burns the respiratory system. Unlike newer chemical agents, mustard can linger in an area for months without breaking down chemically.

Army officials insist that no final decision has been made to build an incinerator at Aberdeen.

A 1988 study concluded that on-site incineration was the safest way of disposing of all the chemical agents and weapons stockpiled throughout the United States, but a "site-specific" environmental study is under way now to see if that conclusion still holds for the Aberdeen stockpile, according to Charles Baronian, the Army's technical director and deputy program manager for chemical demilitarization.

Opponents of incineration contend that the Army needs to look at alternative methods of disposal, such as treating mustard with chemicals to neutralize it. They question the government's "rush to burn." Others say that stockpiles in heavily populated areas such as Aberdeen ought to be shipped to remote areas for disposal, where an accident would put fewer people at risk.

The Army has been testing a $550 million chemical weapons disposal plant on Johnston Island in the Pacific Ocean, about 800 miles southwest of Hawaii. Another plant is under construction at Tooele, Utah.

Even if mustard from Aberdeen could be shipped safely to either plant, there is intense political opposition in both places to taking outside materials, said Mr. Baronian.

Incineration has been shown to be a safe method of disposing of chemical agents, Mr. Baronian contended, noting that in the early 1970s the Army burned mustard without incident at Rocky Mountain Arsenal on the outskirts of Denver.

But Peter Montague, research director with the Environmental Research Foundation in Washington, argued that there are still many unknowns about the environmental impact of incinerating the chemical weapons. He noted that the Chesapeake Bay already is degraded, and he contended that burning mustard will produce toxic byproducts related to dioxin.